Abstract: Lost frame reconstruction is described. A previous good or reconstructed frame may be analyzed to determine a category for the lost frame. A percentage Pi may be associated with the determined category of the lost frame. A top Pi percent magnitude samples may be zeroed out in an excitation of the previous good or reconstructed frame to produce a reconstruction excitation. The reconstruction excitation may be applied to one or more linear prediction coefficients for the previous good or reconstructed frame to generate a reconstructed frame.

Abstract: A method is disclosed for operating a MEMS device having a flap that is movable with respect to a base. The method includes applying a force to the flap to move the flap at least partially out of contact with an underlying base. Means for applying such a biasing force may be incorporated into a microelectromechanical (MEMS) apparatus having a base and a flap with a portion coupled to the base so that the flap may move out of the plane of the base between first and second position. The base may have a cavity with largely vertical sidewalls that contact a portion of the flap when the flap is in the second position Electrodes may be placed on the vertical sidewalls and electrically isolated from the base to provide electrostatic clamping of the flap to the sidewall. The base may be made from a substrate portion of a silicon-on-insulator (SOI) wafer and the flap defined from a device layer of the SOI wafer. The flap may be connected to the base by one or more flexures such as torsional beams.

Abstract: A two-dimensional scanner consists of a rotatable gimbal structure with vertical electrostatic comb-drive actuators and sensors. The scanner's two axes of rotation may be controlled independently by activating two sets of vertical comb-drive actuators. The first set of vertical comb-drive actuator is positioned in between a outer frame of the gimbal structure and the base, and the second set of vertical comb-drive actuator is positioned in between the inner part of the gimbal structure and the outer frame of the gimbal structure. The inner part of the gimbal structure may include a reflective surface, and the device may be used as a mirror. Furthermore, the capacitance of the vertical comb-drives may be measured to monitor the angular position of the mirror, and the capacitive position-monitoring signal may be used to implement closed-loop feedback control of the mirror angle. The two-dimensional scanner may be fabricated in a semiconductor process.

Abstract: A microelectromechanical systems (MEMS) element and a MEMS optical switch are described. The MEMS element comprises a crystalline and moveable element is moveably attached to the substrate. The moveable element includes a perpendicular portion oriented substantially perpendicular to a plane of the substrate. The crystal structure of the perpendicular portion and substrate are substantially similar. The moveable element is capable of motion substantially constrained to a plane oriented substantially perpendicular to a plane of the substrate. In at least one position, a part of a perpendicular portion of the moveable element projects beyond a surface of the substrate. The moveable element may be retained in place by a latch. An array of such structures can be implemented to work as an optical switch. The optical switch may comprise a crystalline substrate and one or more moveable elements moveably attached to the substrate.

Abstract: Methods and apparatus for calibrating a frequency difference between two or more lasers over an extended frequency range as well as optical signal generators that employ such an apparatus or method are disclosed. The lasers are tuned in coordination with respect to one or more readily characterized narrow frequency ranges to characterize one or more tuning parameters of each of the lasers over the extended frequency range. The apparatus may include first and second tuning controllers respectively coupled to the first and second lasers, an optical coupler optically coupled to the first laser and the second laser, a frequency detector coupled to the optical coupler and a controller coupled to the frequency detector and the temperature controllers. The controller may include a processor and a memory containing processor executable instructions for calibrating the two lasers in accordance with the method described above.

Abstract: Disclosed is an apparatus and method for detecting whether rotatable MEMS elements are in the “on” or “off” position. Embodiments of the invention have application in devices switches that employ mirrors that move between an “on” or “off” position, wherein they reflect light from an input fiber into an output fiber in the “on” position, and allow the light to pass in the “off” position. Electrodes are positioned in the device such that the mirrors are close to, and therefor capacitively coupled to, a different electrode depending on whether they are in the “on” or “off” position. This invention is especially useful for switches that already employ electrodes for electrostatic clamping of mirrors in one or more positions, since those same electrodes can be used both to electrostatically clamp the mirrors and to sense their position.

Abstract: A parallel plate diode comprising metal electrodes and semiconductor materials layer contacting said metal electrodes. Two thin plate electrodes made of metal are disposed in parallel, and there is a layer of thin plate semiconductor material sandwiched between the two thin plate electrodes, the concentration of the carriers in the semiconductor material layer is 20% or less than that of the electrons in the metal. One of the metal electrodes is made so as to have a plurality of recesses from its surface into the interior on the side that faces the semiconductor coat layer, the diameter of those recesses is less than 4 micrometers. These recesses are well-shape cavities and an array of the convex portions and concave portions are staggered each other. The cross section of the well shape is circular, square or rectangle. This diode output a current and a voltage in a closed loop circuit without bias voltage or bias current.

Abstract: A method for forming an epitaxial layer involves depositing a buffer layer on a substrate by a first deposition process, followed by deposition of an epitaxial layer by a second deposition process. By using such a dual process, the first and second deposition processes can be optimized, with respect to performance, growth rate, and cost, for different materials of each layer. A semiconductor heterostructure prepared by a dual deposition process includes a buffer layer formed on a substrate by MOCVD, and an epitaxial layer formed on the buffer layer, the epitaxial layer deposited by hydride vapor-phase deposition.

Abstract: A device having a landing pad structure on an underside of a device and method for fabricating same. The device is formed from a device layer with at least one landing pad protruding from an underside thereof. The landing pad is attached to the device layer by a plug passing through an opening in the device layer. The device may be attached to the device layer by one or more compliant flexures, which allow the device to rotate in and out of a plane defined by the device layer. The landing pads are fabricated by forming one or more vias through the device layer. An underlying sacrificial layer is then partially etched to form one or more depressions at locations corresponding to locations of the vias in the device layer. The vias and depressions are then filled with a landing pad material to form a structure having one or more landing pads protruding from an underside of the device layer. The sacrificial layer is subsequently removed to release the device.

Abstract: A multi-layer vertical comb-drive actuator includes a first comb structure having a plurality of first comb fingers and a second comb structure having a plurality of second comb fingers, wherein the first and second comb fingers are substantially interdigitated. The first and second comb fingers may include two or more stacked conductive layers electrically isolated from each other by an insulating layer or an air gap. Alternatively, either the first or second comb fingers may include only one conductive layer. An application of a voltage between the first and second comb fingers causes the second comb structure to move relative to the first comb structure. The present invention includes a 2D-gimble configuration to rotate a movable element along two axis.

Abstract: An optical fourth-harmonic generation system includes a resonant cavity configured to support electromagnetic radiation of a fundamental frequency and a fourth-harmonic generator disposed within the resonant cavity produces electromagnetic radiation of a fourth-harmonic frequency by an interaction with radiation of the fundamental frequency. The fundamental radiation is characterized by a p polarization that is complementary to an s polarization that characterizes the fourth-harmonic radiation. The fourth-harmonic generator has an output facet oriented substantially at a Brewster's angle with respect to the fundamental radiation to separate the fundamental radiation from the fourth-harmonic radiation as they emerge from the output facet.

Abstract: An epitaxial film of a III-V compound may be formed on a non-native substrate by sequentially forming a plurality of epitaxial layers on the substrate at a growth temperature. By cooling the substrate and each sequentially grown epitaxial layer to a sub-growth temperature prior to resumption of epitaxial growth, stress within the sample (due to thermal mismatch between the substrate and the epitaxial layer) is periodically relieved. Sequential epitaxial growth is combined with system etching to provide an epitaxial layer which not only has a lower propensity to shatter, but also exhibits improved surface morphology. Sequential hydride vapor-phase epitaxy using HCl as both source gas and etchant, allows integration of sequential deposition and system etching into a single process.

Abstract: Methods and apparatus for varying and measuring the position of a micromachined electrostatic actuator using a pulse width modulated (PWM) pulse train are disclosed. One or more voltage pulses are applied to the actuator. In each of the pulses, a voltage changes from a first state to a second state and remains in the second state for a time tpulse before returning to the first state. The position of the actuator may be varied by varying the time &Dgr;tpulse. A position of the actuator may be determined by measuring a capacitance of the actuator when the voltage changes state, whether the time t is varied or not. An apparatus for varying the position of a MEMS device may include a pulse width modulation generator coupled to the MEMS device an integrator coupled to the MEMS device and an analog-to-digital converter coupled to the integrator. The integrator may measure a charge transferred during a transition of a pulse from the pulse generator.

Abstract: A method for the production of a crack-free epitiaxial film having a thickness greater than that which can be achieved by continuous epitaxial crystal growth. This epitaxial film can be used as is in a device, used as a substrate platform for further epitaxy, or separated from the initial substrate material and used as a free-standing substrate platform. The method utilizes a defect-rich initial layer that absorbs epitaxially derived stresses and another layer, which is not defect-rich, which planarizes the crystal growth front, if necessary and provides high quality epitaxial region near the surface.

Abstract: Four-port optical circulators and apparatus employing such optical circulators are disclosed. The circulators utilize various arrangements of birefringent elements, polarization rotators and non-reciprocal polarization rotators to route optical signals from a first input/output (I/O) port to a second I/O port, from the second I/O port to a third I/O port, from the third I/O port to a fourth, and from the fourth I/O port to the first I/O port. The number of components and their configuration may be varied depending upon requirements of optical isolation, port configuration, manufacturability, yield and cost. Four-port circulators may be incorporated into an apparatus with optical signal conditioners, such as chirped fiber gratings, wavelength converters or optical amplifiers, optically coupled to one or more of the input/output ports. Alternatively, the circulators may be incorporated into a bidirectional add/drop apparatus with bandpass filters coupled to two of the input/output ports.

Abstract: A method for rotating a combdriven device about an axis uses applied bias force along with applied voltage between first and second comb fingers to controllably rotate the device about one or two axis. One mode of the present invention includes measuring the position of a rotating element and providing feedback to control the angular position thereof by changing bias force and/or drive voltage. The present invention can be employed with prior-art staggered combdrives, single layer self-aligned combdriven devices, and in a broad range of applications in optical telecommunication switching, video, biomedical, inertial sensors, and in storage magnetic disk drives.

Abstract: A method for operating a redundant optical communication network has at least two network transmission paths, assigns first and second protection protocols to switched signals and secondary signals respectively, adds and drops the switched signals and secondary signals on the at least two network transmission paths, makes the switched signals and the secondary signals to counter-propagate along the at least two network transmission paths, therefore, the redundant optical communication network can support different data types and different protection mechanisms.

Abstract: A method of fabricating multi-layer vertical comb-drive actuator that includes a first comb structure having a plurality of first comb fingers and a second comb structure having a plurality of second comb fingers, wherein the first and second comb fingers are substantially interdigitated. The present invention includes masking and etching of a structure that contains these multiple layers, wherein the first and second comb fingers are simultaneously fabricated. The first and second comb fingers may include two or more stacked conductive layers electrically isolated from each other by an insulating layer or an air gap. Alternatively, either the first or second comb fingers may include only one conductive layer.

Abstract: Rotating devices including actuators and position sensors that employ combdrives are described. One design of a combdrive fabricated from a single layer is provided such that, in a nominal state, the two sets of comb fingers are substantially interdigitated according to a predetermined engagement. A rotating element may be attached to a rotatable flexure disposed along an axis and coupled to the comb fingers along with a biasing element attached to the rotating element to cause the comb fingers along with the rotating element to undergo a controlled angular displacement from the initial engagement and in response to feedback from sensing the position of the movable or rotating element. A voltage may be applied between comb fingers to cause the rotating element to undergo further rotation about the axis in a predetermined manner.

Abstract: A device having a landing pad structure on an underside of a device and method for fabricating same. The device is formed from a device layer with at least one landing pad protruding from an underside thereof. The landing pad is attached to the device layer by a plug passing through an opening in the device layer. The device may be attached to the device layer by one or more compliant flexures, which allow the device to rotate in and out of a plane defined by the device layer. The landing pads are fabricated by forming one or more vias through the device layer. An underlying sacrificial layer is then partially etched to form one or more depressions at locations corresponding to locations of the vias in the device layer. The vias and depressions are then filled with a landing pad material to form a structure having one or more landing pads protruding from an underside of the device layer. The sacrificial layer is subsequently removed to release the device.